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Refractive error blindness
Rakhi Dandona1 & Lalit Dandona2
Recent data suggest that a large number of people are blind in different parts of the world due to high refractive
error because they are not using appropriate refractive correction. Refractive error as a cause of blindness has been
recognized only recently with the increasing use of presenting visual acuity for defining blindness. In addition to
blindness due to naturally occurring high refractive error, inadequate refractive correction of aphakia after cataract
surgery is also a significant cause of blindness in developing countries. Blindness due to refractive error in any
population suggests that eye care services in general in that population are inadequate since treatment of refractive
error is perhaps the simplest and most effective form of eye care. Strategies such as vision screening programmes
need to be implemented on a large scale to detect individuals suffering from refractive error blindness. Sufficient
numbers of personnel to perform reasonable quality refraction need to be trained in developing countries. Also
adequate infrastructure has to be developed in underserved areas of the world to facilitate the logistics of providing
affordable reasonable-quality spectacles to individuals suffering from refractive error blindness. Long-term success
in reducing refractive error blindness worldwide will require attention to these issues within the context of
comprehensive approaches to reduce all causes of avoidable blindness.
Keywords: Refractive errors/complications/etiology; Amblyopia/etiology (source: MeSH).
Mots clés: Troubles réfraction oculaire/complication/étiologie; Amblyopie/étiologie (source: INSERM).
Palabras clave: Errores de refracción/complicaciones/etiologı́a; Amblyopia/etiologı́a (fuente: BIREME).
Bulletin of the World Health Organization, 2001, 79: 237–243.
Voir page 242 le résumé en français. En la página 242 figura un resumen en español.
Introduction
Refractive error as a cause of blindness has not
received much attention because many definitions of
blindness have been based on best-corrected distance
visual acuity, including the definition used in the
International Statistical Classification of Diseases and
Related Health Problems (1). However, in many parts
of the world refractive error would become the
second largest cause of treatable blindness after
cataract if blindness were defined on the basis of
presenting distance visual acuity (2–10). Refractive
error is also one of the most common causes of visual
impairment (3–5, 9–13).
Because of the increasing realization of the
enormous need for correction of refractive error
worldwide, this condition has been considered one of
the priorities of the recently launched global initiative
for the elimination of avoidable blindness: VISION
2020 — The Right to Sight (14, 15). For the most
part, refractive error can be easily corrected with
spectacles, which makes it imperative that effective
strategies be developed to eliminate this easily
treatable cause of blindness.
This review presents a summary of the current
and likely future issues related to blindness due to
refractive error.
Definition of blindness
Ref. No. 00-1034
Blindness is defined either in terms of best-corrected
distance visual acuity (the most appropriate refractive
correction) or presenting distance visual acuity (the
individual’s current refractive correction) in the
better eye. The latter definition permits assessment
of blindness due to refractive error, whereas the
former does not. Although a large amount of data are
available on the prevalence of blindness in different
parts of the world (16), data on the prevalence of
blindness due to refractive error are not readily
available because the presenting distance visual acuity
definition is not always used.
Also of importance in the definition of
blindness is the level of visual acuity that is applied.
Visual acuity levels of <3/60 or < 6/60 in the better
eye have been commonly used to define blindness
(2–9). In addition, visual acuity levels <6/60 have
sometimes been used to define blindness, for
example in the USA (10).
Bulletin of the World Health Organization, 2001, 79 (3)
#
1
Consultant, International Centre for Advancement of Rural Eye Care,
L.V. Prasad Eye Institute, Banjara Hills, Hyderabad – 500 034, India
(email: [email protected]); and Doctoral Student, Centre for
Eye Research Australia, University of Melbourne, Melbourne, Australia.
Correspondence should be sent to this author at the former address.
2
Director, International Centre for Advancement of Rural Eye Care,
L.V. Prasad Eye Institute, Hyderabad, India.
World Health Organization 2001
237
Special Theme – Blindness
Magnitude of refractive error
blindness
We carried out a literature search to identify
information from different parts of the world on
the magnitude of blindness due to refractive error
from population-based surveys of blindness published in 1990 or later. The findings are summarized
in Table 1 (2–10).
With blindness defined as a presenting
distance visual acuity < 3/60 in the better eye,
the prevalence of blindness due to refractive error
has been reported to be as high as 0.20% in
Pakistan (2) and India (7), for all age groups in the
population considered together. If blindness is
defined as presenting distance visual acuity <6/60
in the better eye, the prevalence of blindness due to
refractive error in an Indian population was
reported to be 0.36%, including 0.06% from
amblyopia resulting from high uncorrected refractive error (7). These data suggest that about 1 of
every 280 people in the study population were
blind from uncorrected or inadequately corrected
refractive error or from refractive error-related
amblyopia.
A high prevalence of refractive error blindness
(0.59%) was found among a population of Chinese
over-50-years using the definition of presenting
distance visual acuity <6/60 in the better eye (8).
With this definition, the prevalence of blindness due
to refractive error among those aged >40 years in an
Indian study population was reported to be quite high
(1.06%) (7). With blindness defined as a presenting
visual acuity <6/60 in the better eye, the prevalence
of refractive error blindness in the USA among
individuals aged >40 years has been reported to
0.33% among Blacks and 0.24% among Whites (10).
It must be kept in mind, however, that if only older
age groups are considered, the prevalence of
refractive error blindness is likely to be higher
because of cumulative effects, than that for all age
groups taken together.
The available data suggest that in India (7) and
China (8) blindness due to natural refractive error is
more common than that due to aphakia, whereas
blindness due to aphakia is more common in some
African countries (5, 6).
Studies carried out in schools for the blind have
also reported blindness due to refractive error. For
example, uncorrected myopia and aphakia were
responsible for 3% of the blindness among blindschool children in Zimbabwe (17), while uncorrected
aphakia and amblyopia were responsible for 5.1% of
the blindness among blind-school children in
India (18).
Although data on refractive error blindness
have only recently started to become available,
evidence suggests that blindness due to uncorrected or undercorrected high refractive error is a
significant problem in developing and developed
countries alike.
238
Impact of refractive error blindness
Blindness due to uncorrected or inadequately
corrected natural refractive error starts at a younger
age than cataract, which manifests itself in old age (7).
If the impact of blindness due to refractive error is
considered in terms of blind-person-years, a person
becoming blind due to refractive error at a young age,
and which is not corrected, would suffer many more
years of blindness than a person becoming blind
from cataract in old age and would place a greater
socioeconomic burden on society. In the Indian state
of Andhra Pradesh, among the individuals who are
blind currently, the total number of blind-personyears suffered over their lifetime by those blind due
to refractive error was estimated to be about twice
that suffered by those blind due to cataract (7).
Blindness due to natural refractive error can
hinder education, personality development, and
career opportunities, in addition to causing an
economic burden on society. However, the impact
of blindness from myopia may be different from that
from hyperopia, since those blind due to myopia are
likely to have better near vision than those who are so
due to hyperopia. Though there are no data available
on the economic loss as a result of blindness due to
natural refractive errors, it would not be unreasonable
to assume that it is probably significant since a large
proportion of those affected are in the economically
productive age group (7). However, this burden of
economic loss may vary with the type of refractive
error. Since aphakia is a cause of blindness among
older age groups, the economic loss associated with it
is likely to be less than that associated with blindness
due to myopia and hyperopia.
Detection of refractive error
Refractive error can be detected through routine
examination of patients who present to clinics, or
through vision screening of the population at large.
The former approach may work satisfactorily in
developed countries, but the latter is necessary in
developing countries because a large majority of the
population does not have access to reasonable quality
eye care services. Vision screening is most commonly
carried out on schoolchildren, which is a valuable
method of identifying potentially treatable ocular
abnormalities, including blindness due to refractive
error and related amblyopia (19–21). School screening is performed in various ways, including simple
visual acuity assessment by school teachers or
paramedical professionals, and by using computers
to assess vision. In developing countries, schoolteachers have been most commonly used for vision
screening of schoolchildren (19, 20). In recent years,
vision screening has also included preschool children
(21–23). However, current understanding of the
natural history of refractive error and amblyopia is
incomplete, thus limiting the prophylactic potential
of early screening of preschool-age children (24).
Bulletin of the World Health Organization, 2001, 79 (3)
Refractive error blindness
Table 1. Prevalence of blindness due to refractive error reported from population-based surveys in selected countries
Year of
publication
Country
Age groups
studied
(years)
Sample Prevalence
Prevalence of
size of blindness blindness due to
refractive error
Blindness definition 1a
1992
1996
1997
1997
Pakistan (ref. 2)
Turkey (ref. 3)
Lebanon (ref. 4)
Ethiopia (ref. 5)
All ages
All ages
All ages
All ages
29 139
7497
10 48
7423
1.78%
0.40%
0.60%
0.85%
1998
2001
Tunisia (ref. 6)
India (ref. 7)
All ages
All ages
3547
10 293
0.80%
1.34%
Blindness definition 2b
1999
China (ref. 8)
>50
5342
4.37%
2001
2001
Australia (ref. 9)
India (ref. 7)
4744
10 293
0.51%
1.84%
Blindness definition 3c
1990
USA (ref. 10)
2395
2913
1.88%
1.17%
>40
All ages
540 (Blacks)
540 (Whites)
a
Presenting distance visual acuity <3/60 in the better eye.
b
Presenting distance visual acuity <6/60 in the better eye.
c
Presenting distance visual acuity 4 6/60 in the better eye.
d
NA = not available.
Since in developed countries the majority of
children attend schools or preschools, it is relatively
easier to reach them by vision screening programmes.
However, in developing countries many children do
not attend school (25), and they are therefore missed
by vision screening programmes conducted in
schools. This problem can be overcome by the
community vision screening approach.
The community vision screening approach
involves door-to-door surveys by trained field
workers to assess visual acuity and identify people
with vision problems. This is followed by refraction
by trained paramedical ophthalmic staff, provision
of spectacles, and referral to the base hospital if any
surgical or medical management is indicated (26).
This approach is more useful than school screening
because it covers ‘‘school-aged children’’ (instead
of only ‘‘school-going children’’), young adults, and
the older population to identify and treat uncorrected refractive error. Community vision
screening approaches involve more financial and
human resources than school screening approaches, but community screening is likely to be
more useful in dealing with refractive error
blindness in the population, particularly when
implemented as part of a comprehensive eye care
programme (26).
Bulletin of the World Health Organization, 2001, 79 (3)
Type of refractive
error responsible
for blindness
0.20%
0.05%
0.08%
0.04%
0.03%
0.05%
0.10%
0.01%
0.04%
0.05%
Aphakia, natural refractive error
Aphakia
Myopia, hyperopia, aphakia
Aphakia
Natural refractive error
Aphakia
Myopia
Hyperopia
Aphakia
Refractive-error-related amblyopia
0.40%
0.19%
0.11%
0.21%
0.03%
0.06%
0.06%
Myopia, hyperopia
Aphakia
Myopia, hyperopia
Myopia
Hyperopia
Aphakia
Refractive-error-related amblyopia
0.33%
0.24%
NAd
NA
Treatment of refractive error
Most refractive errors are easily treatable by appropriate refractive correction. However, high refractive
error in childhood may lead to amblyopia, resulting in
permanent vision loss if it is not corrected during
early childhood. Refractive correction can be by
spectacles, contact lenses, or refractive surgery.
Spectacles are the most commonly used form of
refractive correction since they are the most
inexpensive and the simplest of the three options;
as such, they are the most appropriate treatment for
refractive error in developing countries. However, all
three forms of treatment for refractive error are
relatively easily available and more affordable to
individuals in developed countries.
Provision of spectacles is currently a challenge
in many developing countries because of issues
related to availability and affordability. There are
often inequities in the availability of spectacles
between urban and rural areas.
Different strategies have been tried to increase
the availability and affordability of reasonable-quality
spectacles, with varying degrees of success. These
include manufacturing low-cost spectacles in developing countries using trained staff, an approach that
has been tried in Africa and Asia (27), use of ready-
239
Special Theme – Blindness
made spectacles with spherical correction for
refractive errors (28), and provision of spectacles at
cost price to the poor. Much work still needs to be
carried out to optimize the logistics necessary to
provide spectacles to all those who would otherwise
be blind without them.
Human resources and infrastructure
Depending on their availability in different parts of
the world, refractive services are provided by various
categories of eye care providers, including optometrists, ophthalmic technicians, opticians, and ophthalmologists.
Adequate numbers of trained personnel for
carrying out refraction are currently not available in
many developing countries (29). To meet this
deficiency, more personnel need to be trained to
perform reasonable-quality refraction, and permanent infrastructure needs to be developed in underserved areas so that adequate refractive services can
be provided in the long term.
Discussion
Even though the treatment of refractive error is
simple and successful, the condition is still responsible for a significant amount of blindness in both
developing and developed countries (2–10). Refractive error is also one of the leading causes of visual
impairment in different parts of the world (3–5, 9–
13). The burden of blindness due to refractive error,
in terms of blind-person-years, is even more
significant than the numbers indicate since refractive
error blindness mostly starts at a young age and
probably causes significant economic and social
burden to societies. Recent data from India suggest
that, in terms of blind-person-years among the
individuals who are blind currently, the burden on
society due to refractive error blindness is about twice
that due to cataract blindness (7).
Definition of blindness
Refractive error as a cause of blindness has been
recognized only recently since many of populationbased surveys of blindness have used best-corrected
distance visual acuity to define blindness. This
definition of blindness misses cases of refractive
error blindness, since it does not take into account the
level of vision with which people actually function in
their daily lives. Those who have poor enough vision
to qualify as ‘‘blind’’ due to uncorrected or
inadequately corrected high refractive error are
considered as ‘‘not blind’’ because their vision
improves with best refractive correction. However,
these people are actually blind because they function
with poor vision due to lack of appropriate refractive
correction. Because refractive error blindness is
missed with the best-corrected distance visual acuity
definition, assessments of blindness should be based
240
on presenting distance visual acuity if refractive error
blindness is to receive its due attention and be
eliminated. This definition would give the ‘‘real’’
magnitude of blindness in a population. Failure to
acknowledge refractive error as a significant cause of
blindness is further underscored by the finding that
some children with poor vision due to uncorrected
high refractive error have been identified in schools
for the blind (17, 18).
Refractive-error-related amblyopia
It is generally believed that blindness due to
refractive-error-related amblyopia is not a significant
problem. However, recent data from India suggest
that this needs to be reconsidered. For example, in a
population-based study in the Indian state of Andhra
Pradesh, 0.06% of the population was blind due to
refractive-error-related amblyopia (7). These data
suggest that in the study population, 20% of those
who had a high enough refractive error to be blind
had developed dense amblyopia resulting in irreversible blindness. Blindness due to amblyopia resulting
from uncorrected high refractive error may therefore
not be insignificant, at least in some populations.
‘‘Index myopia’’
‘‘Index myopia’’ (myopia induced by development
of nuclear cataract) should be kept in mind when
determining blindness due to refractive error. For
individuals blind due to moderate-to-severe nuclear
cataract, placing a high negative dioptre lens in front
of the eye may improve their vision somewhat and
shift the vision category from ‘‘blind’’ to ‘‘not
blind’’. However, the real cause of poor vision in
such cases is cataract (which induced the index
myopia) and not refractive error, and clinically most
of the patients with significantly advanced cataract
would be advised to have surgery even if their
vision improved slightly with a high negative
correction. The caveat here is that there is a danger
of ‘‘overestimating’’ refractive error blindness if
poor vision resulting from cataract-related index
myopia is attributed to refractive error. This would
be a distortion, and could lead to inaccurate
estimates and inappropriate strategies. Such a
distortion would be somewhat analogous to the
previous overestimation of blindness attributed to
cataract in India because detailed dilated eye
examinations were not carried out, resulting in
misclassification of posterior segment blindness as
cataract blindness (30).
Provision of spectacles
It is a major public health failure that so many people
continue to be blind in both developing and
developed countries because they do not have the
appropriate spectacles. The question therefore arises
as to why these people are not able to obtain
refractive correction. In developing countries, the
reasons include a low rate of seeking refractive error
correction (31) and limited access to treatment
Bulletin of the World Health Organization, 2001, 79 (3)
Refractive error blindness
because of generally inadequate infrastructure and
human resources (29). It is surprising that also in
developed countries there is a fairly high level of
refractive error blindness, the reasons for which have
not yet been fully elucidated (32). Attempts at
reducing refractive error blindness need to address
the following major issues: provision of adequate
infrastructure and human resources to detect
refractive error; making affordable spectacles available; and actually dispensing the spectacles.
Comprehensive eye care
It would seem prudent to view the elimination of
refractive error blindness as part of a comprehensive
eye care approach, which would address also the
other major causes of blindness. This would be more
efficient and also facilitate long-term solutions for
reducing blindness. This issue is particularly important in developing countries, where the scanty
infrastructure and human resources have led to
piecemeal approaches to blindness control, and
which more often than not have failed to produce
substantial results. Development of adequate facilities and reasonably trained human resources to
tackle refractive error blindness should therefore be
part of the overall framework to deal with blindness
in a country. Some projects using this approach are
showing success (26), but it needs to be tried on a
much larger scale. Within this framework, particularly
for refractive error, sufficient personnel to carry out
refraction would have to be made available through
good quality training.
Vision screening programmes in the community, including school screening, would probably
make it possible to detect individuals suffering from
refractive error blindness. Such screening programmes need to be implemented on a large scale.
There are several questions that need to be addressed
when planning such programmes, the most important of which are what age groups should be targeted
for screening and how the services would be
provided to those who need them. Reliable data on
the prevalence of blindness due to refractive error
and the distribution of refractive error obtained from
population-based surveys would indicate the groups
that need to be targeted for vision screening to reduce
refractive error blindness. Data on the distribution of
refractive error are available for some populations
(33–46). In developing countries, there is a need to
include all school-aged children in the screening
rather than only school-going children, since many do
not attend school.
Provision of services to individuals who need
them after being identified through vision screening
is as important as the vision screening itself.
Provision of affordable, reasonable-quality spectacles
is crucial for the effective delivery of eye care services.
The emphasis in such vision screening programmes
should not only be on the number of people
screened, but also on the number who experience
substantial improvement of vision with spectacles.
Bulletin of the World Health Organization, 2001, 79 (3)
Aphakia after cataract surgery is also a significant
cause of blindness in developing countries since
many individuals with aphakia do not obtain adequate
spectacles or lose them and do not have them
replaced. These difficulties can be addressed, on the
whole, through provision of cataract surgery with
intraocular lens implantation, which would reduce
the chances of blindness due to aphakia. In addition,
provision of adequate refractive services for those
with aphakia has to be tied with cataract blindness
programmes.
Other issues that need to be addressed include
the following: adequate understanding of the
barriers to providing eye care services; and encouragement of eye health promotion activities. Some
work has been carried out on the assessment of
barriers to cataract surgery, but systematic data on
barriers to refractive correction are quite scanty (31,
32). More research is needed in this area to plan
strategies that would be effective in reducing
refractive error blindness. Eye health promotion
activities, including routine eye examinations, also
need to be encouraged for long-term and sustainable
reduction of blindness. However, in developing
countries such activities would have to be planned
carefully after taking into account the competing
demands on the time and scanty financial resources
of people in these countries.
Recent data suggest that there has been an
increase in the prevalence of myopia in some parts of
the world over the past few decades (34, 35, 41–43).
The reasons for this are not clear but this trend could
result in a higher prevalence of high myopia which, if
not adequately corrected, could result in an increase
in the number of people who are blind due to
refractive error.
Conclusions
Blindness due to refractive error is a substantial
public health problem in many parts of the world. Its
presence implies inadequate eye care services in the
population concerned since treatment of refractive
error is probably the simplest and most effective of
eye care interventions. Elimination of avoidable
blindness due to refractive error requires that the
following be satisfied: a definition of blindness be
used that consistently uses the presenting distance
visual acuity definition; good-quality populationbased data be available on the various aspects of
refractive error blindness, including the barriers to
refractive correction; adequate numbers of personnel be trained to carry out reasonable-quality
refraction, especially in developing countries; effective screening programmes be developed to detect
refractive error blindness in the population; provision of affordable reasonable-quality spectacles be
facilitated through development of permanent
infrastructure for eye care in the underserved areas;
and in developing countries a rapid shift be made
241
Special Theme – Blindness
towards cataract surgery with intraocular lens
implantation.
Long-term success in reducing refractive error
blindness worldwide depends on attention being paid
to these issues within the context of comprehensive
approaches to reduce all causes of avoidable
blindness. n
Acknowledgements
The study was supported by the Hyderabad Eye
Research Foundation, Hyderabad, India and by
Christoffel-Blindenmission, Bensheim, Germany.
Rakhi Dandona is a recipient of the R. B. McComas
and Hugh Noel Puckle Scholarships from the
University of Melbourne, Melbourne, Australia.
Résumé
Vices de réfraction et cécité
D’après des données récentes, un grand nombre de
personnes sont aveugles dans différentes parties du
monde en raison d’un vice important de réfraction qui
n’est pas convenablement corrigé par le port de lunettes.
C’est seulement depuis peu que les vices de réfraction
sont reconnus comme cause de cécité, la cécité étant de
plus en plus souvent définie par l’acuité visuelle à
l’examen. A la cécité due aux vices importants de
réfraction qui surviennent naturellement, s’ajoute la
correction optique inadaptée de l’aphakie, qui est
également une cause considérable de cécité dans les
pays en développement. Dans une population, l’existence d’une cécité due aux vices de réfraction indique
que les services de soins oculaires généraux sont
insuffisants, vu que la correction optique des vices de
réfraction est peut-être la forme la plus simple et la plus
efficace de soins oculaires. Des stratégies telles que les
programmes d’examen de la vision doivent être mises en
œuvre à grande échelle pour déceler les sujets atteints de
cécité due à un vice de réfraction. Dans les pays en
développement, il faut former le personnel en nombre
suffisant pour que la prestation du diagnostic et de la
correction des vices de réfraction soit de qualité
satisfaisante. Il faut aussi développer des infrastructures
correctes dans les secteurs mal desservis du monde pour
faciliter la logistique de l’approvisionnement en lunettes
de qualité convenable à un prix abordable, pour les
personnes atteintes de cécité due à un vice de réfraction.
Le succès durable, à l’échelle de la planète, du recul de la
cécité due aux vices de réfraction exigera une attention à
ces questions dans le cadre des approches intégrées
visant à réduire toutes les causes de cécité évitable.
Resumen
Ceguera por errores de refracción
Datos recientes llevan a pensar que un gran número de
personas de distintas partes del mundo están ciegas
como consecuencia de errores de refracción no
corregidos debidamente. La identificación de esos
errores como causa de ceguera es algo reciente, y se
debe al uso cada vez mayor de la agudeza visual de
presentación como criterio de definición de la ceguera.
Además de la ceguera por graves errores naturales de
refracción, otra importante causa de ceguera en los
paı́ses en desarrollo es la corrección inadecuada de la
afaquia tras la cirugı́a de la catarata. La presencia de
casos de ceguera por errores de refracción en una
población indica que los servicios oftalmológicos son en
general inadecuados en esa población, toda vez que el
tratamiento de esos errores es quizá la forma más
sencilla y eficaz de atención oftalmológica. Es preciso
aplicar a gran escala estrategias idóneas, por ejemplo
programas de cribado de la vista, para detectar a las
personas que sufran ceguera por errores de refracción, y
es necesario que en los paı́ses en desarrollo se capacite al
suficiente personal para corregir esos errores de manera
aceptable. Asimismo, en las zonas del mundo subatendidas se debe desarrollar una infraestructura adecuada
para facilitar la logı́stica que permite ofrecer lentes
asequibles de calidad razonable a quienes sufren
ceguera por errores de refracción. Para conseguir reducir
eficazmente a largo plazo esa forma de ceguera en todo
el mundo habrá que prestar atención a estas cuestiones
en el contexto de enfoques amplios tendentes a reducir
todas las causas de ceguera evitable.
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